Some wireless protocols, such as Bluetooth®, include a power control mechanism which involves a receiving station signalling to the transmitting station to request that the transmitted power is increased or decreased. A determination of when such a request is required is made at the receiving station based on packets received from the transmitting station. The power control mechanism attempts to prevent the transmitted signal power from going too low, in which case the transmitted signal will not be received by the transmitting station. In addition, the power control mechanism attempts to prevent the transmitted signal power from being too high, which wastes electrical power and results in the transmitting signal interfering with others over a larger range than required.
In an existing receiving station, sampled received signal strength indication (RSSI) values are put through a discrete exponential filter which is adjusted per packet. The filter smoothes (or averages) the received values, which vary with time because the transmitting station hops between frequencies and different frequencies may suffer different losses in transmission from the transmitting station to the receiving station. The speed of the filter is slow in order to avoid falsely reducing the output value, which might trigger a request to be sent to the transmitting station, when the radios hop to a frequency which is subject to fading. Fading is a term used to describe a dramatic drop in received power around a particular frequency which is caused by destructive interference from multi-path signals.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known methods of power control.